Drilling rigs used for the drilling of oil and gas wells typically include a supportive rig floor positioned over a well. A derrick extending vertically above the rig floor supports a traveling block which can be raised and lowered within the derrick, the traveling block supporting a tubular drill string. During drilling operations, a drill bit on the end of the drill string is conveyed into a well and is manipulated within the well via the drill pipe. The drill pipe is raised and lowered within the well utilizing the drilling rig derrick.
When installing drill pipe or other tubular pipe into a well, such pipe is typically installed in a number of sections of roughly equal length called “joints”. As such pipe penetrates farther and farther into a well, additional joints of pipe must be added to the ever lengthening “string” or “drillstring” in the rig derrick. Thus, a typical drillstring comprises a plurality of sections or joints of pipe, each of which has an internal, longitudinally extending bore. During drilling operations, a drill bit along with other desired equipment is attached to the lower or distal end of said drill string.
In the most basic sense, rotary drilling operations typically involve attaching a drill bit on a lower end of a drillstring to form a drilling tool and rotating the drill bit along with the drillstring into a subterranean formation to create a well bore through which subsurface formation fluids may be recovered. In another method of drilling, coiled tubing may be used instead of jointed pipe and the drill bit may be rotated using a downhole motor.
During drilling operations, a fluid known as drilling mud or drilling fluid is normally pumped down bore of the drill pipe, and circulated up the annular space which is formed between the external surface of said drill pipe and the internal surface of the wellbore. The basic functions of drilling mud are: (1) to cool and lubricate the drill bit and downhole equipment during drilling operations; (2) to transport pieces of drilled-up rock and other debris from the bottom of the hole to the surface; (3) to suspend such rock and debris during periods when circulation is stopped; (4) to provide hydrostatic pressure to control encountered subsurface pressures; and (5) to seal the porous rock in the well with an impermeable filter cake.
As circulated drilling mud returns to the earth's surface and is pumped out of a well, the mud contains pieces of broken, drilled-up rock and other solid debris known as “cuttings” or “drill cuttings”. In most cases, an effluent mud stream flowing out of a well, together with associated drill cuttings, is directed to one or more devices which are designed to separate such drill cuttings from the mud. Such devices include, but are not limited to, shale shakers, desanders, desilters, hydrocyclones and centrifuges.
Shale shakers are essentially screens that are used to separate drill cuttings from the drilling mud. In many cases, shale shakers utilize a series of screens arranged in a tiered manner relative to each other and are often made to vibrate in order to increase the quality of such separation. The bulk drilling mud passes through the screens by gravity, while the predominantly solid cuttings are inhibited from passing through and instead pass over the end of the screens. Certain shale shakers are designed to filter coarse material while other shale shakers are designed to remove finer particles from the drilling mud. Shale shakers and other similar devices are frequently necessary to efficiently separate drill cuttings from drilling mud.
Once drill cuttings and other debris have been separated from the bulk mud stream flowing out of a well, it is necessary to dispose of such cuttings. Unfortunately, the disposal of drill cuttings can present a number of different problems. Often, the most economical way to dispose of drill cuttings would simply be to discharge said cuttings directly into the surrounding environment, such as in a mud pit or discharged from an offshore platform or drill ship into the water. Even though drill cuttings leaving a shale shaker or other separation device may have been separated from a well's effluent mud stream, such cuttings nonetheless can include entrained mud and other fluids which could be damaging to the environment.
In order for drilling mud to accomplish its intended objectives, it is often necessary to control certain characteristics of such drilling mud. Chemicals and/or other additives are often mixed into such drilling muds for control of a certain parameter. Common drilling mud additives include gelling agents (e.g., colloidal solids and/or emulsified liquids), weighting materials, and other chemicals which are used to maintain mud properties within desired parameters. Although drilling mud has historically been water-based, improved results have been obtained using oil-based or synthetic-based muds, especially in severe drilling environments. Many of these additives, oil-based muds and synthetic-based muds can be environmentally harmful. Thus, it is often undesirable and a violation of environmental regulations to release such fluid-laden cuttings directly into the surrounding environment.
In order to avoid environmental contamination and comply with applicable governmental regulations, drill cuttings are frequently transported from a drilling rig to an off-site facility for disposal. In order to accomplish such off-site disposal, drill cuttings are generally loaded into boxes or other storage containers for transportation away from the rig. While this solution can be generally functional, it is not without significant problems.
One major problem associated with the off-site disposal of drill cuttings is increased cost. In most cases, special equipment is needed to move fluid-laden drill cuttings from a rig's shale shakers to another location on the rig where storage containers are loaded. Such equipment is often in the form of complicated and elaborate conveyors, augers and/or vacuum units. Moreover, large numbers of storage containers must be rented or purchased in order to accommodate such cuttings. All of this added equipment and labor increases the costs associated with the drilling process. This additional equipment can present logistical and/or safety problems on many rigs.
Another problem associated with off-site disposal of drill cuttings is environmental impact. Such off-site disposal of drill cuttings does not necessarily guarantee an overall reduction or elimination of environmental contamination. Cuttings containers must be transported to a rig, loaded with cuttings, and thereafter moved to an off-site storage facility. Trucks, vessels or other pollution-emitting means of transportation must typically be employed to transport the containers to and from the rig. As a result, the overall impact on the environment of offsite disposal can be significant.
Attempts have been made to clean drill cuttings in order to remove surface contaminants prior to discharge of such cuttings into the environment. For example, certain cuttings recovery and treatment devices utilize separate cells having low speed agitators to stir a mixture of cuttings and cleansing surfactants. The cuttings are transferred from one cell to the next where additional agitation and cleansing takes place. Thereafter, a slurry of cleansed drill cuttings and surfactant is pumped from the cells to a vibrating screen operation in which most of the surfactant is removed and recovered for later use. In some cases, a portion of the surfactant solution, which is rich in fine drill cuttings and adherent drilling fluids, is run through one or more hydrocyclone separators which discharge the fine drill cuttings in solution separated from the larger, cleansed drill cuttings.
However, attempts at washing or otherwise treating drill cuttings on location have also proven to be problematic. Frequently, existing methods of washing drill cuttings require large amounts of equipment, which can cause space problems on most drilling rigs and add to the overall expense of a drilling project. Further, such cuttings washing systems utilize surfactants or other solutions which must be disposed of or, at a minimum, kept out of the surrounding environment. Perhaps most significantly, washed drill cuttings are often not clean enough for discharge directly into the surrounding environment.
A treatment fluid may be used in a variety of subterranean operations. As used herein, the term “subterranean operation” is defined to mean any operation that requires the performance of some action or procedure below the surface of the earth, including, but not limited to, actions or procedures performed in the course of recovering oil, gas, and/or other substances from a formation below the surface of the earth. As used herein, the term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof, but instead refers to any use related to a subterranean operation in conjunction with a desired function and/or for a desired purpose. For example, a fluid may be used to drill a well bore in a subterranean formation or to complete a well bore in a subterranean formation, as well as numerous other purposes.
Accordingly, a need exists for a means to dispose of drill cuttings in a cost-effective and environmentally sound manner.